Ultrasonic attenuation coefficients were measured in mammalian [beef] liver for frequencies ranging from 0.5-10 MHz and for a range of sample preparations. Certain preparative procedures greatly increased the low-frequency attenuation coefficient due to the introduction of bubbles into the sample. The low-frequency attenuation was reduced by storage at low temperatures or by pressurization, each caused the bubbles to go into solution, resulting in an attenuation coefficient that was a simple power function of frequency. Absorption coefficients of in vitro and in vivo samples were similar and showed much less dependence on sample preparation than the attenuation measurements. Properties of carefully prepared in vitro samples are apparently indicative of the in vivo properties.